b)Discovery of a derelict with a damaged interior
The interior was shot full of immense holes in the walls, ceiling and machinery as though the ship had been riddled with impossible corrosive acid or even someone had been firing what would be in that story's universe, something like a military disintegrator in there. Dead at the controls is the skeleton of the alien pilot.

However the idea of the giant skeletal remains of an alien pilot seem very much borrowed from Mario Bava's film Planet of the Vampires discovered in a chamber where an audio played is found that when activated plays endless alien utterances, but in Alien the giant alien's remains bear no resemblance to the human form and are discovered seated in a control chair.

On a console on the walls, there is a machine, and on it, a small bar moves steadily back and forth, sliding noiselessly in its grooves. This is where the transmission is coming from.

The original Planet of the Vampires script contained a transmitter created by the disembodied spirits on the planetoid to lure space travellers to the planet.

The Space Jockey's remain

c)A giant skeleton
Ron Cobb did the illustration of the skeleton, which later becomes knows as the Space Jockey, and Ron's design was just perfect in Dan O'Bannon's eyes.

It had a very large cranium, and four or five eye sockets, a very small jawbone with no teeth to speak of.

He expected it to look horrible when it is seen in the film, but then one looks at it a bit closer and finds that it didn't have large teeth or mandibles or any other thing that are characteristic of a carnivore, and then one might begin to imagine it as some totally non-violent herbivorous creature sailing around space

d) Transmission's revelations
The transmission turns out to be an automatic recording which has been repeating for God knows how long.

The question is, what killed the crew?

Scrawled onto the console before the dead pilot is a symbol, a hastily scrawled triangle.

Clearly he was trying to leave a message.

e) Sighting of a pyramid
When the explorers are puzzling over the meaning of the triangle, the storm outside momentarily clears up, enabling them to see the horizon.

The on the cliffs is seen is pyramid, instantly suggestive of the triangle.

Is this what the pilot was trying to indicate?

They go to explore it.

The idea in Alien that they discover an alien creature and the discover something else that led to a further mystery, in terms of Dan O'Bannon's version of the script where the inside of the pyramid and the derelict ship were two separate places, it was one of the more specific things that he was thinking about from Nigel Kneale's work.

In one description shaped like a huge toadstool (Dan O'Bannon's online version early Alien script)

And another description a lobster(Dan O'Bannon's DVD version of the early Alien script.)

Dan O'Bannon: Shot
full of immense holes as though the ship had been riddled with
impossibly corrosive acid. Dead at the controls is the skeleton of the
alien pilot"(Dan O'Bannon's Unseen Alien, Starburst 15, p42)

Dan O'Bannon: The
giant alien's remains bear no resemblance to the human form and are
discovered seated in a control chair. On a console on the walls,
there is a machine, and on it, a small bar moves steadily back and forth, sliding noiselessly in its grooves. This is where the transmission is coming from" (Dan O'Bannon's online version early Alien script)

Dan O'Bannon : Ron
Cobb did the skeleton - what they later call the Space Jockey - and it
was just perfect. It had a very large cranium and four or five eye
sockets. Very small jawbone - no teeth to speak of. Of course, I
expected it to look horrible when you see it in the film, but then if
you looked at it a bit closer, you'd discover that it didn't have the
large teeth or the mandibles or any other thing that are characteristic
of a carnivore - and then maybe you'd begin to imagine it as some
totally non-violent herbivorous creature sailing around space." (Dan O'Bannon interviewed in Cinefex 1, p64)

Dan O'Bannon: It
turns out to be an automatic recording, which has been repeating for
God knows how long. The question is: what killed the crew? Scrawled
onto the console before the dead pilot is a symbol, a hastily scrawled
triangle. Clearly he was trying to leave a message.

Dan O'Bannon:While
they are puzzling over the meaning of the triangle, the storm outside
clears up momentarily, enabling them to see to the horizon. There on the
cliffs is a pyramid, instantly suggestive of the triangle. Is this
what the pilot was trying to indicate? They go to explore it.(Dan O'Bannon's Unseen Alien, Starburst 15, p42)